HEPA Filtration Units – Why It’s More Important Than Ever for Schools to do Their Homework

Published 03/29/2021
By Christian Weeks
Target Air Changes for Schools

From Dr. Fauci to the CDC to ASHRAE, experts recommend employing HEPA filters as part of a layered approach to COVID-19 mitigation including strategies such as masking, hand washing and improved ventilation and filtration.

Given the CDC’s recent guidance update recommending that K-12 schools can reduce social distancing from 6ft. to 3ft., and new reports of highly transmissible variants of the COVID-19 virus, it is important to re-examine the role HEPA filtration can play in helping schools reopen safely. Last week we shared a statement on the CDC’s new guidance. This week we offer this blog post with tips for schools looking to employ HEPA filters to mitigate the transmission of COVID-19.

Deploying local HEPA filters is necessary when central HVAC systems do not exist or cannot support high efficiency, MERV 13 of higher, filters on the central HVAC system. Many schools, including most older school buildings, need local HEPA filters.

The good news is that Federal stimulus funds can be used to purchase local HEPA filters. The key, of course, is to ensure that these stimulus funds are used for durable solutions that will achieve the desired COVID mitigation goals. Ideally, investments in HEPA filters can also provide value post-COVID, especially for frontline communities exposed to higher levels of pollution.

Here are 6 recommendations in choosing HEPA filters for your school along with links to a few useful guides.

  1. Stick with proven HEPA filtration technology. Do your homework and do not be swayed by other solutions that sound too good to be true (such as technologies using ionization). Be sure to look specifically for HEPA or True HEPA designation. Other naming conventions likely indicate less than 99.99% cleaning efficiency.
  2. Target school air changes per hour
    Courtesy Harvard-CU Boulder Portable Air Cleaner Calculator for Schools

    Make sure you have a robust enough product. Smaller portable units are inexpensive, but are they getting the job done? The Harvard T.H. Chan School of Public Health recommends 5-6 air changes per hour (ACH) for schools. This means all the air in a classroom will be exchanged with clean air every 10-12 minutes. A good rule of thumb for sizing filters is 300 cubic feet per minute (CFM) of airflow for every 500 ft2. According to one recent study, in order to achieve high air exchange rates and homogeneous mixing in the entire room it can be of advantage to install several smaller purifier units. This handy tool from the Harvard School of Public Health can be used for sizing.

  3. Placement matters. As more research/analysis is conducted, experts recommend locating HEPA filters as close to the middle of the room as possible, elevated up off the ground. This will maximize the amount of air moving through the HEPA filter. For classrooms with 20-30 people, experts also say fixed devices are more appropriate than portable units. This is because fixed devices, such as ceiling-mounted HEPA filters, can be centrally located, are often higher powered than portable units, and are quieter to operate, especially when installed in ceilings. Additionally, as this New York Times visualization shows, when windows are closed contaminate concentrations are highest where warm air rises near the ceiling. On a more practical level, fixed units are out of reach of young children and avoid trip hazards from cords.
  4. Noise is a key issue. If units are too loud, teachers or students will turn them off or adjust the fan speed below a level of effectiveness. Schools that purchased loud portables are finding the fan noise disrupts instruction and are now having to replace their initial purchase with quieter HEPA units. Ceiling-mounting puts air filters up and away from “ear-level” cutting down on noise concerns considerably.

“With respect to air cleaners for airborne pathogens, there is a very clear hierarchy of performance,” said Raefer Wallis, global indoor air quality expert and Founder of RESET. “At the very top, we find ceiling-mounted filtration systems that allow for a very high level of control in specific areas because they are ducted and unobstructed by objects in a room. This is extremely important for issues like COVID-19, where aerosolized viruses can be removed at the source. The next level down is portable filters, which are 20-50% less effective than their ceiling mounted counterparts mainly due to challenges with placement in a space. Last is traditional central filtration systems, which force virus particles to travel a long distance prior to being removed.”

  1. Be sure to flag other locations of concern beyond the classroom. Evaluate environments where there are high concentrations of aerosols such as music rooms, staff break rooms, group bathrooms and locker rooms.  Units should also be evaluated for large density gathering places such as auditoriums, and especially cafeterias where students will be unmasked.
  2. Make a durable investment. Small, portable HEPA filers can be inexpensive but will they last beyond the pandemic? Because fixed, ceiling mounted units are out of the way and quieter to operate, they are a better long-term solution that will help improve indoor air quality in schools during and after the COVID-19 pandemic, particularly for schools in front line communities exposed to higher levels of pollution. Rather than investing stimulus funds in a short term solution that will likely end up in a closet after the pandemic – or worse a dumpster – we recommend investing stimulus funds in a durable long term air cleaning solutions.

The American Rescue Plan is delivering much needed funding to schools to pandemic-proof their spaces and improve infrastructure. It makes good sense to make a lasting investment versus a short-term, disposable option. Once the pandemic is in our collective rear-view mirror, fixed HEPA units will remain part of a school’s infrastructure protecting staff and students from pollution, allergens, and seasonal flu and other contagious viruses. Schools in front-line communities, in city centers, near highways, or those in wildfire-prone areas will benefit from lower pollution levels, decreased exposure to smoke, and other asthma triggers addressed by HEPA filters.

It is important for schools to remember as they select HEPA filtration units – do your homework, check your math, and invest wisely. Click here to learn more about the enVerid True HEPA Air Purifier for schools, or click below to read our Definitive Guide to Improving Classroom Air Quality for COVID-19 Mitigation.

Read the Definitive Guide to Classroom Air Quality

Christian Weeks

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